The relationship(s) between the immune response system and muscular dystrophy is being studied in the Storrs strain of hereditary muscular dystrophic chickens in which two immunodeficiencies, reduced IgG levels and an abnormal splenic T suppressor cell population, have been identified. The reduced IgG levels in the Storrs strain have been determined to be due to a strain difference. Studies on the abnormal T cell suppressor population suggests that this immune defect may influence the severity of muscle deterioration in the muscular dystrophic chickens. Current studies are directed at further characterization of the abnormal T cell suppressor population by immunological, biochemical and genetic analyses. Characterization will include cell type identification, analyses of mechanism of suppression, establishment of suppressor cell expression throughout muscular dystrophic chicken development, and further analyses of the relationship of the abnormal suppressor cell population to the pathogenesis of the muscular dystrophy trait. Effects of thymectomy and thymus cell transplants on the severity of the muscular dystrophy phenotype will be examined.